The present invention relates to a cover assembly for a vehicle air bag, and more particularly to a cover assembly for use at the interior of a steering wheel on the driver""s side of a vehicle which incorporates a contoured cover element, an underlying membrane horn switch and a contoured reaction plate beneath the membrane horn switch. The reaction plate includes an upper surface contoured to substantially match the interior contour of the cover element such that a substantially uniform distance is maintained between the cover element and the horn switch between the upper and lower edges of the cover element.
It is well known in motor vehicles to provide an air bag module for protecting a vehicle occupant. It is also generally known to provide an air bag module including an inflatable restraint cushion and an inflator for discharging inflation gas to inflate the cushion upon sensing predetermined vehicle conditions such as deceleration exceeding a certain level. It is also known to provide air bag modules including pressure activated membrane horn switches disposed in sandwiching relationship between a molded depressable cover element and a substantially rigid reaction plate. Such air bag modules are illustrated and described in U.S. Pat. No. 6,236,309 to Haag and U.S. Pat. No. 5,762,365 to Worrell et al. the contents of which are incorporated by reference as if fully set forth herein.
The membrane horn switches conventionally comprise two very thin sheets having conductive coatings which are normally separated by thin spaces. Pressure on the switch forces the conductive surfaces together so as to complete a circuit and thereby actuate the horn. Typically, membrane horn switches are less than about one millimeter in thickness. To actuate the horn, the driver must sufficiently compress the cover member so as to apply the requisite pressure to the membrane horn switch to bring the opposing conducting surfaces together.
The use of a reaction plate in mounted relation to the cover element generally below the membrane horn switch provides a substantially solid surface against which the membrane horn switch can be compressed to actuate the horn. In practice, the reaction plate is typically held in place below the cover element and the membrane horn switch by a plurality of mounting posts which extend away from the interior surface of the cover element through aligned apertures in both the membrane horn switch and the reaction plate. The ends of the posts are melted together to heat stake the reaction plate to the cover. The interior surface of the cover element may also incorporate horn actuating projections which normally extend partially across the space between the interior surface of the cover element and the membrane horn switch. The use of such horn actuating projections reduces the distance the cover element must be compressed in order to actuate the membrane horn switch.
In the past, the reaction plates utilized have been of a generally planar configuration thereby forming a generally flat surface in operative opposing relationship to the interior surface of the cover element. While such a planar surface provides substantially uniform support to the membrane horn switch, the distance between the membrane horn switch and the interior surface of the cover element may vary across the module if the interior surface of the cover element is not also planar.
Recently, cover elements have become more stylized leading to a greater degree of curvature in the outer surface of the cover element facing the occupant. In addition, the use of so called xe2x80x9csingle shotxe2x80x9d injection molding procedures to form the cover elements from a single layer of material has gained popularity. In such xe2x80x9csingle shotxe2x80x9d constructions it is generally desired for the cover element to have a substantially uniform thickness in the regions overlying the, membrane horn switch so as to promote substantially uniform compressibility in those regions. However, in a contoured construction the incorporation of a substantially uniform thickness gives rise to a corresponding contour across the inner surface of the cover element. Such an inner surface contour gives rise to a variation in the distance between the interior surface of the cover element and the membrane horn switch. This differential distance may require the cover element to be depressed to a greater extent in some locations in order to contact and actuate the membrane horn switch.
The present invention provides advantages and alternatives over the prior art by providing an air bag cover assembly including a cover element of generally profiled configuration and including one or more mounting posts extending downwardly from the interior surface of the cover element. A reaction plate of generally contoured construction substantially matching the contour of the cover element is held in place at a position below the inner surface of the cover element. A membrane horn switch is disposed in sandwiched relation between the reaction plate and the inner surface of the cover element.
According to one aspect of the present invention, an air bag cover assembly is provided including a cover element having a curved exterior show surface and a curved interior surface and wherein a plurality of mounting posts extend downwardly away from the interior surface. A reaction plate of substantially curved contour substantially matching the contour of the inner surface of the cover element is held in place at a position below the inner surface of the cover element by heat staking of the mounting posts. A membrane horn switch is captured between the reaction plate and the interior surface of the cover element such that the distance between the interior surface of the cover element and the membrane horn switch is substantially uniform across the cover assembly.
According to another aspect of the present invention, the reaction plate includes a plurality of apertures for acceptance of mounting posts therethrough. The mounting posts preferably include a shoulder portion which engages a substantially planar shoulder stop in surrounding relation to the post acceptance apertures at the upper surface of the reaction plate. A plurality of protuberant boss elements are disposed across the underside of the reaction plate substantially at the post accepting apertures to facilitate heat staking at those locations. Preferably, the reaction plate is curved in an arched configuration substantially between the forward and aft edges adjacent the upper and lower edges of the air bag module.
The construction according to the present invention is believed to promote an enhanced degree of uniformity in the force required to actuate the membrane horn switch at various locations beneath a curved cover while at the same time facilitating proper alignment and attachment of the component parts thereby improving the manufacturing process. Accordingly, the present intention is believed to provide a useful advancement over the prior art.